Apparatus for treating plated strip metal



March 5, 1940. J. F. FERM APPARATUS FOR TREATING PLATED STRIP METALFiled Dec. 27,1958

INVENTOR JbH/v FIE-RM.

ATTORNEYS.

Patented Mar. 5, 1940 UNITED STATES ArrAaATUs ron TREATING PLATED s'rnn'METAL John F. Fcrm, Midland, Pa., assignor to Pitts-- burgh CrucibleSteel Company, Pittsburgh, Pa., a corporation of'PennsylvaniaApplication December 27, 1938, Serial No. 247,871

4 Claims.

This invention relates to apparatus for treating plated strip metalhaving a coating of a lower melting metal on a base metal of highermelting point, such as tin coated or plated sheet 6 or strip steel, forimparting to the coating, a

smooth, impervious surface of high lustre approximating mirrorbrightness. The invention is particularly applicable for imparting amirror bright finish to coatings applied by a process ofelectrodeposition.

This application is a continuation in part of my application Serial No.224,101, filed August 10, 1938, now Patent No. 2,141,382.

Strip steel may be coated with tin by a process of electrodepositionfroma tin plating bath. The process may be made continuous by feeding thestrip from a roll through the plating bath and out again. The tincoating thus applied to the strip has, however, a dull, matteappearance, requiring further treatment for imparting the mirror finishrequired by the trade. This may be imparted by passing the plated stripthrough a hot oil bath of appropriate temperature and othercharacteristics, such as a bath of palm oil maintained at about 475 to500 F., whereby the tin coating softens and fuses to form the requisitebright, impervious surface, free from pin holes. However, upon sobrightening the coating, the tin must be cooled and hardened rapidly ina non-oxidizing atmosphere to retain its brilliance and prevent surfacecrystallization or spangling. Air cooling is, therefore, unsatisfactoryfor this reason and for the additional reason that the molten surface ofthe tin is marred by air jets incident thereon. Hardening may beaccomplished by passing the strip rapidly from the hot oil bath into acool oil bath maintained at a suiliciently low temperature to harden thetin quickly, for example, about 135 to 150 F.

A problem is presented, however, in passing the strip through the hotoil bath and thence into the cool oil bath in such manner that the tincoating will not be exposed to atmospheric or oxidizing conditions or tomechanical marring, while the tin is in a molten or plastic state causedby immersion in the hot oil bath. If, for example, the known expedientwere employed of passing the strip by means of a series of feed r orguide rolls, first down into the hot oil bath, thence up out of thisbath and over and down into the cool oil bath, the strip must ofnecessity pass over a number of such rolls while the tin is molten orplastic, whereby the rolls would 5 leave imprints in the brightenedsurface and thus destroy the smooth, mirror finish. Likewise, unless anappropriate reducing admosphere were maintained above the baths, the tincoating would be subject to oxidation causing a dulling 60 of thesurface during passage of the strip between the baths. The provision forand maintenance of such a reducing atmosphere adds both to thecomplexity of the apparatus and to the expense of its operation.

In accordance with the invention of my above mentioned parentapplication, defects of the character aforesaid are overcome byarranging the hot and cool oil baths in tanks situated adjacent oneanother and by interconnecting the two with a duct such that the stripmay be fed in a straight line from a point outside the hot oil bath,through the hot bath and thence through the duct into the cool oil bath.To this end, the strip is arranged to pass over a feed roll just priorto immersion in the hot oil bath, but does not encounter any additionalfeed roll or other mechanical element until it has reached such a pointin the cool oil bath that the coating has been well hardened, at whichpoint the strip passes over a second feed roll and out of the bath.

As is further explained in said application, the fact that the hot andcool baths are in direct liquid contact with each other through the ductinterconnecting the two, introduces an additional problem of preventingthe establishment of rapid thermal exchanges between them such as wouldbring them quickly to a common equilibrium temperature. If, for example,the baths were merely separated by a partition having an orifice thereinor by a duct extending horizontally between the tanks, pressuredifferences between the hot and cold baths are bound to establishthemselves at various elevations within the orifice or duct due to thedifferent density of the hot oil in comparison with the cool oil, inconsequence of which convection currents will be' established betweenthe baths bringing them rapidly to a common temperature and thusrendering the brightening process inoperative.

This diificulty is overcome in accordance with the invention of saidapplication, by arranging the interconnecting duct in inclined relation,preferably such that it slopes downwardly from the hot oilto the cooloil tank, and to such a degree that its entry into the cool oil bath issituated entirely below its entry into the hot oil bath. With thisarrangement the surface level of the hot oil bath will so adjust itselfin relation to the surface level of the cool oil bath by appropriatetransferences of liquid between the two through the duct, that the hotand cool oil baths will be in approximate pressure equilibrium withinthe duct at a level intermediate between the levels at which the ductenters the hot and cool oil bath respectively. By virtue of thisarrangement, the hot and cool oil baths will contact each other in ahorizontal surface within the duct, the opposing pressures at all pointsof which are the same, so that there is little tendency for establishingconvection currents in the manner aforesaid thereby to destroy thediflerence in temperature of the baths. Also, owing to the downwardslope of the duct from the hot to the cool oil bath, the hot and henceless dense oil will be situated within the duct above the cooler andhence denser and more viscous oil thereby further stabilizing thetendency of the normally adjust themselves to a condition of substantialsurface equilibrium as above explained, is determined primarily by thedensity of the hot oil in relation to that of the cool oil, the actionbeing analogous to the equilibrium adjustment of water and mercury inopposite sides of a U tube. Since the density of the hot oil is somewhatless than that of the cool oil, the hot and cool oil baths will normallyadjust themselves to a condition of equilibrium within the inclined ductsomewhat above the median level between its openings into the two baths,which is to say, that the cool oil will extend up to and somewhat abovethe median level with the hot oil occupying the upper remaining portionof the duct.-

In some instances, however, it is desirable that the cool oil extend toa greater height within the duct than would result with the arrangementabove described. For example, in the brightening of electroplated tinnedstrip, it is desirable that the tin coating be hardened or frozen asquickly as possible as it passes out of the hot oil bath into the duct,which action is expedited by increasing the cool oil level in the duct.In accordance with the present invention, the cool oil level may beestablished and maintained at any desired elevation in the duct byconnecting a horizontally disposed equalizing pipe between the cool oiltank and the inclined duct at the level in question. With thisarrangement, 0001 oil will fiow from the cool oil tank through thehorizontally disposed equalizing pipe and into the inclined duct untilthe cool oil level therein has been brought up'to the level of theequalizing pipe.

The arrangements above described have proved quite effective in practicefor the brighteningof tinned strip and the like, where the speed of thestrip through the duct is not too great. If, however, the rate of feedof the strip is high, it

tends to carry a portion of the hot oil along with the hot oil bath, theoil thus withdrawn being I passed through an oil cooler, returned thenceunder pressure to the jets in the cool oil tank.

With the system asthus arranged, some care must be taken with respect tothe point at which the suction pipe is connected to the inclined duct,since if the connection is located either wholly or partially above theupper cool oil level in the duct, hot oil will be withdrawn from theduct, passed through the oil cooler and returned to the coololl bath.This is undesirable because the hot oil thus withdrawn is replaced by0001 oil returning through the duct to the hot oil bath, and alsobecause it'results in an unnecessary increase in the cost of fuel andpower required to maintain the hot oil bath at its appropriatetemperature and to cool the oil passing through the cooler to the propertemperature.

The system of my parent application offers little flexibility withrespect to location of the junction between the suction pipe and theinclined duct, inasmuch as it requires locating the junction below theupper cool oil level as determined by the relative densities of the hotand cool oil. With the present invention on the other hand, the suctionpipe may be connected at any desired level to the inclined duct, bymerely connecting the equalizing pipe above referred to, to the same orahigher point along the inclined duct. In this way it is assured thatonly cool oil will be withdrawn by the suction pipe irrespective of itspoint of connection to the inclined duct.

Referring now to the accompanying drawing:

Fig. 1 shows schematically in longitudinal section, the brighteningbaths and interconnecting duct as arranged in accordance with my parentapplication aforesaid;

Fig. 2 is a. similar view employing the equaliz- 7 4 more of the detailsof the baths as actually employed in commercial operation and the mannerof feeding coated strip therethrough for brighten- V Referring to Fig.l, the hot oil bath is shown at I, the cool oil bath at 2, and theinclined duct at 3 having openings 4 and 5 into the hot and cool oilbaths respectively. The coated strip to be brightened is fed into thehot oil bath I, thence through the inclined duct 3, and through and outof the cool oil bath 2, in a manner explained more in detailhereinafter. For offsetting the tendency to carry hot oil along with itinto the cool oil bath when fed rapidly, cool oil is directed underpressure by nozzles ii into the opening 5 of the duct 3 into the cooloil bath, the cool oil thus injected being in turn withdrawn at a pointfurther along duct 3 by the suction pipe 1 extending to an oil cooler 8and thence through a pressure line 9 to nozzles 6.

Representing the densities of the hot and cool oil by 112 and d1,respectively, and the surface elevations of the hot and cool baths by712 and hl, thepressure heads of the two baths are in equilibrium at butone elevation .X, where:

dgh3-d h d,d

The surface elevations will so adjust themselves by interchange ofliquid between the baths that the equilibrium surface X will normallylie somewhat above the medium level between openings .4, 5 as determinedby the relative densities of the hot and cool oil in accordance with theabove equation. The level X is thus more or less inflexibly determinedwith the apparatus arranged as in Fig. 1, and necessitates connectingthe suction pipe I at a point well down in duct 3 to assure that itsopening into the duct will be below the upper cool oil level X, andhence will notsuck hot oil into the oil cooler 8.

With the system as modified in accordance with the present invention asshown in Fig. 2, there is added a horizontally disposed equalizing pipel0, connected between the cool oil bath 2 and the inclined duct 3, at alevel at which it is desired to establish and maintain the upper cooloil level in the duct. With the arrangement of Fig. 2, cool oil willflow from the cool oil bath 2 and through the equalizing pipe Iuntil'the equilibrium level X between the hot and cool oil baths isbrought up to the level of the equalizing pipe. In this way, the uppercool oil level in duct 3 may be brought quite close to the opening 4 ofthe duct into the hot oil bath thereby to expedite the hardening orfreezing of the fused coating as the plated strip passes from the hotoil bath through the duct. Moreover, the suction pipe 1 extending to theoil cooler 8, may, with this arrangement,'be connected to duct 3 at anylevel desired by merely connecting the equalizing pipe to the duct atsubstantially the same or a higher level as shown, thereby to assurethat the upper cool oil level will be above the suction pipe junctionand only cool oil withdrawn.

Referring now to Fig. 3 disclosing a commercial form of apparatus forbrightening tin-coated steel strip and the like in accordance with theinvention, the strip 20, having previously been coated by passagethrough an electroplating bath and otherwise been appropriately cleanedand prepared for the brightening bath, is fed over a roll'2l, and thencein a straight line, through a hot oil bath 22 contained in tank 23, andthrough duct 24 interconnecting the hot oil bath with a cool oil bath 25contained in tank 26, whereupon the strip passes under a second feedroll 21 immersed in the cool oil bathand having its periphery inalignment with the exit from the duct as shown. Thereafter the strippasses out of the cool oil bath and between a pair of squeegee rolls 23,made of soft rubber or the like, for removing the greater portion of theoil adhering to the strip. The duct 24 extends downwardly from the hotoil to the cool oil tank as explained and to such a degree that itsentrance into the cool oil bath is situated wholly below its entrance tothe hot oil bath.

In order to prevent the hot oil from being carried alongby the stripinto the cool oil tank, cool oil is directed into the entrance of duct24 into the cool oil tank by nozzles 29, fed by a pressure line from theoil cooler 3 l, into which oil is drawn off from duct 24 by the suctionpipe 32. For maintaining the upper cool oil level X above the junctionbetween pipe 32 and duct 24, one or more horizontally disposedequalizing pipes 33 are provided which connect duct 24 with the cool oiltank 25 at the level X. Preferably a pair of such equalizing pipes areprovided and connected to opposite sides of the duct 24 as seen in planview. The cool oil circulates through the duct and oil cooler as shownby arrows.

As an additional aid in maintaining a sharp dividing surface X in theduct between the hot oil and cool oil and also to maintain the hot oilbath at the proper temperature, the hot oil may .be' to maintain thecirculation, the I shows a, gravity. circulation obtained by extendingpipe 31 between the heater and the hot oil tank at the surface level ofthe oil as shown.

In order to maintain the cool oil bath at its proper temperature, anintake line 39 may be provided which draws off from near the top of tank25 the warmer layer of cool oil collecting at the surface of the bathand passes it into the cooler 3|, whence 'it is returned to the baththrough nozzles 29.

, I claim:

1. Apparatus for treating plated strip metal comprising: a, first tankfor containing a hot bath to a preselected level, a second tank forcontaining a cool bath to a preselected level, a first duct joining saidtanks below said levels and having an opening into the second tanksituated below its opening into the first tank, and a second ductextending from a point on said first duct intermediate said openingsto apoint on said second tank below the bath level thereof and above theopening of said first duct thereinto, and means external to said firsttank and duct for conveying said strip metal therethrough and into sa dsecond tank.

2. Apparatus for treating plated strip metal comprising: a first tankfor containing a hot bath to a preselected level, a second tank forcontaining a cool bath to a preselected level, a first duct joining saidtanks below said levels and having an opening into the second tanksituated below its opening into the first tank, a second duct extendingfrom' a point on said first duct intermediate said openings to a pointon said second tank below the bath level thereof and above the openingof said first duct thereinto, means for injecting cool liquid of saidbaths into said first duct and for withdrawing liquid therefrom, thepoint of injection being closer to the second tank than the point ofwithdrawal, and the latter being no closer to the first tank than thepoint of connection of said second duct to said first duct,

and means external to said first tank and duct for conveying said stripmetal therethrough and into said second tank.

3. Apparatus for treating plated strip metal comprising: a firsttank forcontaining a hot bath to a preselected level, a second tank forcontaining a cool bath to a preselected level, an inclined duct joiningsaid tanks below said levels and having an opening into the second belowits entry into the first, a horizontally disposed duct extending fromsaid second tank to a point on said inclined duct intermediate saidopenings, and means external to said first tank and inclined duct forconveying said strip metal therethrough and into said second tank.

4. Apparatus for treating plated strip metal comprising: a first tankfor containing a hot bath to a preselected level, a second tank forcontaining a cool bath to a preselected level, an

inclined duct joining said tanks below said levels and having an openinginto the second below its entry into the first, a horizontally disposedduct extending from said second tank to a point on said inclined ductintermediate said openings, means for injecting cool liquid of saidbaths into said inclined duct at its opening into said second tank andfor withdrawing liquid 'fromsaid duct at an elevation not exceeding thatof said horizontal duct, and means external to said first tankandinclined duct for conveying said strip metal therethrough and intosaid second tank.

JOHN F. mm.

